This invention relates to an ion implanter, and it especially relates to the ion implanter suitable for mass separation by implanted oxygen in which oxygen is implanted into a silicon wafer.
An example of a conventional ion implanter is disclosed in Japanese Patent Laid-open No. 1-189845, in which a heat transfer material such as an electrically conductive rubber is provided between a wafer and a holder therefor so as to hold a periphery of the wafer in order to suppress overheating of the wafer caused by being implanted with an ion beam. The wafers are arranged on a disk shaped holder.
In recent years, such an ion implanter used for mass separation by implanted oxygen has been researched and developed rapidly. In such an ion implanter, an oxygen ion is implanted at a predetermined depth in the silicon wafer which is heated to several hundred degrees, and after that, a buried layer of SiO.sub.2 is formed in the silicon wafer by performing a thermal annealing treatment.
In a case that a semiconductor device is constructed on such substrate, it becomes possible to realize a high-speed device with less power consumption.
In the conventional ion implanter which is used in a semi-conductor process, ions are implanted with an ion dose of 10.sup.14 to 10.sup.15 /cm.sup.2. However, in the wafer for mass separation by implanted oxygen, ions should be implanted with the ion dose of 10.sup.17 to 10.sup.18 /cm.sup.2. When the periphery of the wafer is held with a holder, the periphery of the wafer is not implanted with the oxygen and the holder is sputtered so as to form a contaminated material.
Furthermore, it is neccessary for the wafer to be implanted while being heated to a temperature of several hundred degrees. The wafers arranged on the disk are supported with a stopper etc. utilizing centrifugal force without supporting the periphery of the wafer, and a stress concentration or a temperature irregularity arises on the wafer by centrifugal force generated when the stopper turns, and thereby the quality of the wafer is deteriorated.
Furthermore, because more than 100 to 1000 times the number of ions in a conventional case are implanted in this ion implanter, contamination of the wafer should be reduced sufficiently.
Therefore, deflection magnets are provided in order to prevent contaminating substances sputtered from the mass separation. Further, the perpendicular disk mounting structure needs to be installed horizontally, and the device including the disk becomes very large-sized.